Downhole tools are used for operations inside boreholes of oil and gas wells. Downhole tools operate in a very harsh environment and must be able to withstand inter alia corroding fluids, high temperatures and high pressure.
To avoid unnecessary and expensive disturbances in the production of oil and gas, the tools deployed downhole have to be reliable and easy to remove from the well in case of a breakdown. Tools are often deployed at great depths several kilometers down the well, and removing jammed tools are therefore a costly and time-consuming operation.
Well tools are often part of a larger tool string containing tools with different functionalities. A tool string may comprise both transportation tools for transporting the tool string in the well and operational tools for performing various operations downhole, e.g. centralising tools for centralising the tool or tool string in the borehole, driving units for moving the tool or tool string in the borehole and anchoring tools for anchoring the tool or tool string in the borehole.
The use of tools and/or units with extracting members for engaging the borehole wall has potential risk of jamming in the borehole in case of a breakdown. Extreme conditions such as very high pressures, high temperatures and an acidic environment therefore place high demands on mechanical mechanisms in downhole tools.
The above often results in a minimum use of such tools downhole to avoid unwanted breaks in production times. Therefore, a need exists for downhole tools that are relatively fail-safe and thus extractable from the borehole, also in case of a breakdown.